The present invention relates to a loop antenna used for a data processing apparatus having a radio communication function for conducting radio transmission and reception between the data processing apparatus and a removable data storing medium having a radio communication function, and thereby conducting predetermined data processing such as data transmission and reception with the removable data storing medium. The present invention further relates to the removable data storing medium including this loop antenna.
In general, in a radio communication system for conducting communication using radio waves, it is necessary to use radio waves each having a strong electric field strength in order to conduct communication stably without being affected by its environment such as noise. Because of the stipulation of the radio law, however, it is impossible to radiate a radio wave having an unlimited strong electric field strength from a data processing apparatus. In the radio law, therefore, it is permitted to radiate a certain fixed strong radio wave for a specific frequency. However, the present frequency is strictly stipulated, and sufficient care is necessary for its use.
Assuming that the above described specific frequency has a wavelength .lambda., .lambda./2.pi. is located near a measurement distance of 3 m stipulated by the radio law. When calculating the strength of a radiant electric field, it is typically difficult to make the theoretical calculation coincide with actually measured values when the distance is in the vicinity of .lambda./2.pi.. Furthermore, the environment of measurement also exerts a great influence. In other words, if an antenna is designed on a desk on the basis of various conditions and a measurement is actually conducted in the vicinity of 3 m, then a value largely different from the design value is obtained, and the radio law cannot be satisfied in many cases.
In other words, in a removable data storing medium having a loop antenna, it is desirable to send a signal with an electric strength as strong as possible. However, the electric strength is regulated by the radio law. Therefore, it is desirable to make an adjustment and ship the medium as a storing medium having the very highest electric field strength the regulation range will permit. If the electric field strength is calculated in a design stage and actual measured data is derived, then a portion other than the antenna portion functions as an antenna, and a very large difference occurs between the theoretical value and the actual value. In such a state that the electric field strength cannot be controlled accurately, therefore, there is a problem that it is impossible to design and ship the medium as a storing medium having the very highest electric field strength the radio law will permit.